Confusion about OnCalculate's documentation

[Soewono Effendi]

I'm a bit confused of this documentation found here:

https://www.mql5.com/en/docs/basis/function/events#oncalculate

I quote it here:
"
OnCalculate

The OnCalculate() function is called only in custom indicators when it's necessary to calculate the indicator values by the Calculate event. This usually happens when a new tick is received for the symbol, for which the indicator is calculated. This indicator is not required to be attached to any price chart of this symbol.
"

What does this suppose to tell us:

This indicator is not required to be attached to any price chart of this symbol.

?

I mean, no indicators are required to be attached to any price chart of any symbol, right ?

Any insight is appreciated.

[William Roeder]

You can call iCustom for any symbol/TF.The indicator does not be attached to any chart.

[Vladislav Boyko]

Soewono Effendi:
What does this suppose to tell us:

What they're probably saying is that an indicator can be attached to another indicator's subwindow. Logically, it's hard to call another indicator's subwindow a price chart.

I drop the Custom Moving Average into the Momentum subwindow and apply it to the "First Indicator's Data":

In the Indicator List, it is clearly visible that the MA is attached to another indicator's subwindow, not to the price chart.

[Alain Verleyen]

That means OnCalculate() is triggered even if this indicator is not attached to the price chart of the used symbol.

That concerns call by iCustom. You can have the iCustom call in a code running on a chart X, but using symbol Y as parameter in iCustom. OnCalculate will be triggered by ticks on symbol Y not symbol X.

[Ryan L Johnson]

William Roeder #:
You can call iCustom for any symbol/TF.The indicator does not be attached to any chart.

Alain Verleyen #:

That means OnCalculate() is triggered even if this indicator is not attached to the price chart of the used symbol.

That concerns call by iCustom. You can have the iCustom call in a code running on a chart X, but using symbol Y as parameter in iCustom. OnCalculate will be triggered by ticks on symbol Y not symbol X.

I agree.

To avoid any further potential confusion, symbol Y must be in the Market Watch window.